1. Field of the Invention
This invention relates to an ignition timing controlling device for an internal combustion engine of a pressure indication detecting type.
2. Description of Background Art
It is known that during the operation of an internal combustion engine changes in the internal pressure of the combustion chamber occur as shown by curve A in FIG. 1. If an ignition system is triggered at an ignition angle .theta..sub.IG, then air fuel mixture is ignited with an ignition delay .theta.d. Thereafter, the cylinder internal pressure follows a process wherein it rises suddenly and then is reduced, passing a maximum pressure peak Pmax (hereinafter referred to as pressure indicating peak).
It is known that the angular position of a crank at the pressure indicating peak is related to a condition in which an engine exhibits its maximum output power. It was experimentally ascertained that the crank angular position of the pressure indicating peak at which the maximum output power can be provided is 12 to 13 degrees after the top dead center (hereinafter referred to as ATDC) as shown in FIG. 1. Thus, an ignition timing controlling device of the pressure indication detection type wherein the ignition timing .theta..sub.IG is controlled such that the pressure indicating peak may coincide with an ideal peak range of ATDC 12 to 13 degrees is already known, for example, by Japanese Patent Publication No. 49-29209.
Such an ignition timing controlling device directly detects an internal pressure of a cylinder and obtains pressure indicating peak position data at each cycle of an engine from a pressure indicating signal indicative of the cylinder internal pressure. The device then compares the pressure indicating peak position data with data of an aimed position in order to cause a lead or a lag of the ignition timing at each engine cycle.
A controlling system for such an ignition timing controlling device as described above wherein an ignition timing is decided depending upon an average value of pressure indicating peak position changes, while ignoring a peak position in a misfire cycle, and so on in order to stabilize operation of an engine is already proposed in Japanese Patent Application No. 60-175182 filed by the present inventor.
However, in such an ignition timing controlling system, the stability of operation of an engine is satisfactory but the responsiveness during transition, such as during sudden acceleration, is not always satisfactory.
During normal operation of an engine, the change of the internal pressure of a cylinder presents a maximum peak at or around the top dead center as described above. However, when either the engine or an indicative pressure detecting signal system thereof is in an abnormal condition, the indicative pressure signal does not exhibit such a change as shown by the curve in FIG. 1. A method of detecting such an abnormal condition is already known by Japanese Utility Model Laid-Open No. 59-49788 wherein an abnormal condition is detected from a changing manner of the indicative pressure peak value within one engine cycle.
Meanwhile, when it is intended to obtain an ignition timing controlling device of the indicative pressure detecting type which can be used both for a 2-cycle engine and a 4-cycle engine, it is necessary to detect suction and exhaust strokes of the 4-cycle engine as so-called waste firing cycles. However, since such a waste firing cycle is not an abnormal condition, it cannot be detected by the art of Japanese Utility Model Laid-Open No. 59-49788 mentioned above.